Protective electrochemical

Lapique F, Valentin G, Storck A (1993) Electrochemical engineering for environmental protection, Electrochem Processing, Innovations and Progress, April 21-23, Glasgow... 

S. de Souza, J. E. Pereira da Silva, S. I. Cordoba de Torresi, M.L.A. Temperini, and M.R. Torresi, Polyaniline based acrylic blends for iron corrosion protection, Electrochem. Solid-State Lett., 4, B27-B30 (2001). 

Several factors in the explanation given in this section are important and will be used later to explain how we measure and stop corrosion. The electrical current flow, and the generation and consumption of electrons in the anode and cathode reactions are used in half-cell potential measurements and cathodic protection. The formation of protective, alkaline hydroxyl ions is used in cathodic protection, electrochemical chloride removal and realkalization. The fact that the cathodic and anodic reactions must balance... 

Electrochemical treatments - cathodic protection, electrochemical chloride extraction and electrochemical realkalization are designed to shift the potential of the steel. This effect may be permanent in the case of cathodic protection or temporary but quite long term in the case of the other two techniques. 

One of the major issues facing any consultant or owner of a structure suffering from chloride or carbonation induced corrosion is what form of repair to undertake. As we have seen from the previous sections there are coatings, sealants, membranes and enclosures, specialized patch repair materials, options for total or partial replacement, impressed current and galvanic cathodic protection, electrochemical chloride removal, realkalization, electro-osmosis and corrosion inhibitors. These can be applied to structures suffering different degrees of corrosion due to chloride attack or carbonation or a combination of these two. Each treatment will have implications for the future maintenance requirements, time to next major intervention and ultimate service life of the structure. 

The structures programme was entirely concerned with corrosion of reinforced concrete bridges suffering from salt induced corrosion. Its work on structures covered physical assessment, cathodic protection, electrochemical chloride removal, physical and chemical methods of rehabilitating bridge components and a methodology of bridge... 

Elimination of chromate treatment of metal sur ces has spurred the investigation of conducting polymer sur ce protection. Electrochemical polymerization as well as chemical polymerization (37) and a solvent free process... 

Figure 8.16 shows an equivalent electrical circuit that simulates the pipeline cathodic protection depicted in Figure 8.9. Both pipeline and sacrificial anode (galvanic anode or inert anode) are buried in the soil of uniform resistivity. The pipehne is connected to the negative terminal and the anode to the positive terminal of an external power source (battery). The arrows in Figure 8.16 indicates the direction of the ciurent flow from the anode to the pipehne. The electron flow is also toward the pipehne to support local cathodic reactions and the protechve current (Ip) flows from the pipehne to the power supply. The soil becomes the electrolyte for complehng the protective electrochemical system or cathodic protechon circmt [24].

Electrochemical chloride extraction. A further technique, applicable to existing concrete structures that have been contaminated with chlorides, involves the electrochemical removal of these harmful ions. The hardware involved is similar to that involved in cathodic protection. Electrochemical extraction of chloride ions is achieved by establishing... 

Highly protective layers can also fonn in gaseous environments at ambient temperatures by a redox reaction similar to that in an aqueous electrolyte, i.e. by oxygen reduction combined with metal oxidation. The thickness of spontaneously fonned oxide films is typically in the range of 1-3 nm, i.e., of similar thickness to electrochemical passive films. Substantially thicker anodic films can be fonned on so-called valve metals (Ti, Ta, Zr,. ..), which allow the application of anodizing potentials (high electric fields) without dielectric breakdown. 

The protective quality of the passive film is detennined by the ion transfer tlirough the film as well as the stability of the film with respect to dissolution. The dissolution of passive oxide films can occur either chemically or electrochemically. The latter case takes place if an oxidized or reduced component of the passive film is more soluble in the electrolyte than the original component. An example of this is the oxidative dissolution of CrjO ... 

Baeckman W v, Schenk W and Prinz W 1997 Handbook of Cathodic Corrosion Protection Theory and Practice of Electrochemical Protection Processes (Flouston, TX Gulf)... 

Material Protection. The graft copolymers of ethylene sulfide on polyethyleneimine can be used as an antifouHng anticorrosion substrate for iron (439). PEIs or their derivatives are also used in electrolysis baths as brighteners in the electrochemical deposition of metals (440,441). 

Cathode and insulator walls are less subject to severe electrochemical attack. In the case of the cathode wall, this is because of the reducing conditions which prevail, and in the case of the insulator wall, because the wall nominally carries no current. However, certain surfaces of cathode and insulator walls are anodic with respect to other surfaces, because of the axial electric field present in the generator, and these surfaces do require protection against electrochemical attack. 

The main cause of anode wear is electrochemical oxidation or sulfur attack of anodic surfaces. As copper is not sufficiently resistant to this type of attack, thin caps of oxidation and sulfur-resistant material, such as platinum, are bra2ed to the surface, as shown in Eigure 15a. The thick platinum reinforcement at the upstream corner protects against excessive erosion where Hall effect-induced current concentrations occur, and the interelectrode cap protects the upstream edge from anodic corrosion caused by interelectrode current leakage. The tungsten undedayment protects the copper substrate in case the platinum cladding fails. 

The resistance to corrosion of some alloy sheet is improved by cladding the sheet with a thin layer of aluminum or aluminum alloy that is anodic to the base alloy. These anodic layers are typically 5—10% of the sheet thickness. Under corrosive conditions, the cladding provides electrochemical protection to the core at cut edges, abrasions, and fastener holes by corroding preferentially. Aircraft skin sheet is an example of such a clad product. 

W. C. Gardiner, in T. R. Beck and co-workers, eds.. Electrochemical Contributions to Environmental Protection, The Electrochemical Society Symposium Series, Princeton, N.J., 1972, p. 16. 

Cathodic Protection This electrochemical method of corrosion control has found wide application in the protection of carbon steel underground structures such as pipe lines and tanks from external soil corrosion. It is also widely used in water systems to protect ship hulls, offshore structures, and water-storage tanks. 

Anodic Protection This electrochemical method relies on an external potential control system (potentiostat) to maintain the metal or alloy in a noncorroding (passive) condition. Practical applications include acid coolers in sulfuric acid plants and storage tanks for sulfuric acid. 

Use and Uimitations of Electrochemical Techniques A major caution must be noted as to the general, indiscriminate use of all electrochemical tests, especially the use of AC and EIS test techniques, for the study of corrosion systems. AC and EIS techniques are apphcable for the evaluation of very thin films or deposits that are uniform, constant, and stable—for example, thin-film protective coatings. Sometimes, researchers do not recognize the dynamic nature of some passive films, corrosion produc ts, or deposits from other sources nor do they even consider the possibility of a change in the surface conditions during the course of their experiment. As an example, it is note-... 

The active and passive electrochemical processes on which present-day corrosion protection is based were already known in the 19th century, but reliable protection for pipelines only developed at the turn of the 20th century. 

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